1. Field of the Invention
This invention relates generally to image forming apparatuses such as electrophotographic copiers, printers and the like, and more particularly to novel assemblies and methods for controlling toner release agent application in such devices.
2. Background Art
In electrophotographic imaging (or xerography), it is well-known to uniformly charge a photoreceptor (e.g., a belt or a drum) to form electrostatic latent images corresponding to original images on a charge retentive surface of the photoreceptor. The selective dissipation of the charge leaves a latent charge pattern on the photoreceptor corresponding to the areas of the original images not exposed by radiation.
After the latent images are formed, toner particles are deposited on the photoreceptor to develop the electrostatic latent images. Next, the developed images are transferred by contact to a media substrate (e.g., paper, transparency, and the like). The media substrate containing the transferred image is then passed between a pressure roller and a fuser roller to permanently fuse the toner images to the substrate.
During fusing, the area of contact or deformation between the pressure roller and the fuser roller is called the xe2x80x9cnip.xe2x80x9d The substrate is moved through the nip with the toner image contacting the fuser roller. Preferably, to promote proper fusing at least one of the pressure and fuser rollers is heated, and at least one of the rollers is coated with an elastomer such as silicone rubber or a resin such as Teflon(copyright). Due to heat build up in the rollers, however, the toner image may adhere to the rollers instead of fusing with the substrate as desired. These xe2x80x9cleftoverxe2x80x9d toner images may be unwittingly transferred from the rollers to a subsequent media substrate passed between the rollers, and may also be passed between the rollers.
One approach to substantially preclude xe2x80x9cleftoverxe2x80x9d toner images has been to apply a toner release agent, such as a microscopic film of low surface energy silicone oil, on the fuser roller such that the toner release agent and the toner images are transferred to the media substrate. Thus, none of the toner images are retained by the pressure or fuser rollers.
Prior art approaches for applying the toner release agent to the fuser roller include mounting an oil roller in abutting relation to the fuser roller such that during operation oil is transferred from the oil roller to the fuser roller. Other devices utilize a system of rollers to transfer oil to the fuser roller. For example, U.S. Pat. No. 5,202,734 discloses a sump for supplying oil to a meter roller, and an oil roller in working contact with a fuser roller. The meter roller and the oil roller work in tandem to transfer oil from the sump to the fuser roller.
Prior art apparatus have several significant limitations and disadvantages. First, the continuous contact maintained between the oil roller and the fuser roller causes excessive oil buildup on the fuser roller during periods of inactivity, which results in excessive oil consumption. Excess oil on the fuser roller not only saturates the media substrate, it can also substantially reduce the working life of the fuser roller and the oil roller.
Prior art approaches to solve this problem have focused on removing excess oil by mounting a blade in working contact with the fuser roller or the pressure roller. However, this solution merely removes the unwanted oil; it does not prevent excessive oil consumption. Moreover, the blade itself causes roller wear, and the blade must be repositioned over time to compensate for wear between the oil roller and the blade. Further, the blade must also be replaced when it becomes worn.
In view of the foregoing, a need exists for a simple, low cost, low maintenance apparatus for controlling toner release agent application in an image forming apparatus.
The present invention relates to a system for applying a toner release agent to a fuser roller within an image forming apparatus. The present invention utilizes a simple, low-cost, reliable thermally-activated actuator subassembly to selectively apply the toner release agent to a fusing unit in the image forming apparatus. The present invention not only conserves the toner release agent, it also increases the imaging quality and prolongs the working life of the image forming apparatus.
An image forming apparatus includes an imaging subsystem for forming images on a media substrate, such as a tone-on-tone electrophotographic imaging apparatus. The imaging subsystem includes, for example, a photoreceptor, a series of print stations operably associated with the photoreceptor to form a developed image thereon, a transfer charger operably associated with the photoreceptor, and a fuser roller.
The image forming apparatus also includes a supply roller for selectively applying the toner release agent onto the fuser roller or other roller. The supply roller is selectively moveable between a first position where the supply roller engages the fuser roller and communicates a toner release agent thereto, and a second or disengaged position where the supply roller does not contact the fuser roller. A thermally-activated actuator subassembly including, for example, a pair of shape memory alloy (SMA) members is provided for controlling engagement and disengagement between the supply roller and the fuser roller. The apparatus is configured such that when a working temperature of the image forming apparatus is at or about a critical temperature (corresponding to the binary activation temperature of the SMA members), the SMA members pull the supply roller into engagement with the fuser roller to transfer the toner release agent from the supply roller to the fuser roller. Conversely, the fuser roller and the supply roller become disengaged when the working temperature of the apparatus falls below the critical temperature.
The present invention also includes several methods. First, a method is disclosed for applying a toner release agent to an electrophotographic imaging device. Also, a method is disclosed for printing toner images on a substrate such that all of said toner images are substantially transferred from the photoreceptor to the substrate.
The present invention conserves the toner release agent by eliminating consumption during inactivity or when the working temperature of the apparatus falls below the critical temperature, eliminates the need for the oil removal blade, and provides a simple, low cost, low maintenance solution with few moving parts.
Other advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.